Add gzip size badge

Author: OliverJAsh

README.md

@@ -5,6 +5,7 @@
 [![npm downloads](https://img.shields.io/npm/dm/react-sortable-hoc.svg)](https://www.npmjs.com/package/react-sortable-hoc)
 [![license](https://img.shields.io/github/license/mashape/apistatus.svg?maxAge=2592000)](https://github.com/clauderic/react-sortable-hoc/blob/master/LICENSE)
 [![Gitter](https://badges.gitter.im/clauderic/react-sortable-hoc.svg)](https://gitter.im/clauderic/react-sortable-hoc)
+![gzip size](http://img.badgesize.io/https://npmcdn.com/react-sortable-hoc/dist/umd/react-sortable-hoc.min.js?compression=gzip)
 
 ### Examples available here: <a href="#">http://clauderic.github.io/react-sortable-hoc/</a>